Carbon nanotube (CNT) fibers have demonstrated significant promise as field emission (FE) cathodes due to their large aspect ratios and high electrical and thermal conductivities. They can potentially be used as FE cathodes in a wide range of applications, including compact radiation sources, electron guns for ring and linear accelerators, and vacuum nanoelectronics. CNT fibers are also extremely flexible and do not lose conductivity when bent. This allows for their arrangement in various cathode geometries other than the typical free standing vertical emitter.
Carbon nanotube (CNT) fiber-based emitters have shown great potential to deliver stable, high current beams for various potential applications. However, because of joule heating, traditional CNT field emitters are heated to high temperatures during field emission; it is important to improve the thermal management of such emitters to increase their reliability and prevent premature failure.
The current state of the art cathode material for use in High Power Microwave (HPM) devices is made from graphite fiber. The devices are made by a technique called flocking, whereby the stiff and rigid graphite fibers are electrostatically implanted into an epoxy base. This makes a graphite fiber carpet of vertically-aligned fibers that may be used as a cathode in HPM systems.
Prior art CNT fiber emitters are typically mounted vertically on a substrate, i.e. the CNT fibers are orthogonal to the substrate, in order to take advantage of the high field enhancement factor due to their high aspect ratio. The tips of the fibers are cut either mechanically or by a laser. However, the mechanically-cut tips usually introduce rough edges with dangling fibrils (see FIG. 1). Laser cutting largely reduces the tip roughness, however, the fiber tips are still spread out at the ends, i.e. frayed ends. The rough edges of the frayed ends and tip spread are undesirable. They lead to non-uniform emission and uneven temperature distribution and hotspots at the fiber tips.